UDC 547.972Metabolites from Phoma sp., a phytopathogenic fungus, were exploited for their herbicidal potential. The phytotoxic compound isolated was identified as anhydropseudophlegmacin-9,10-quinone-3c-amino-8c-Omethyl ether on the basis of spectral data. The isolated pigment was tested for its herbicidal potential against the prominent weeds of Central India, where a positive result was obtained.Weeds are important pests, which cause economic losses in agricultural and forestry systems and serious ecological problems, and which are capable of altering the ecosystem, displacing native flora and fauna [1]. Plant pathogenic microbes have been a novel and lucrative source of a wide range of bioactive compounds with herbicidal potential. Phoma is a well-known phytopathogen responsible for many diseases in plants and is known to produce an array of bioactive extracellular phytotoxic compounds [2,3]. Anthraquinones have also been isolated from Phoma foveata [4], while other fungi too have been reported to exhibit biological activity [5]. As part of our search for potential herbicidal agents, presently we describe the isolation, purification, and characterization of a pigment exhibiting herbicidal potential against, the prominent weeds of Central India. This is the first report where a pigment, i.e., anhydropseudophlegmacin-quinone, exhibits herbicidal potential against the target weeds.The red pigment, R f 0.30, was obtained as an optically active light yellow powder, mp 232qC, [D] D 25 + 33.14q (c 0.91;MeOH), in a yield of 2 u 10 -2 % of fresh weight of the fungus. The electron spray ionization mass spectrum (ESI-MS) displayed a molecular ion peak at m/z 523 corresponding to the molecular formula C 30 H 21 O 8 N. This formula suggests the presence of a dimeric octaketide structure, whereas the long-wavelength absorption at 500 nm in the electronic spectrum suggested the presence of an anthraquinone chromophore. The IR absorption bands at 3482, 3208, and 1610 cm -1 indicated the presence of hydroxyl, amino, and quinone carbonyl groups in the compound. The 1 H NMR spectrum of the pigment revealed the presence of seven aromatic protons, four of which showed a doublet at G 6.91, 6.85, 6.66, and 6.94 ppm, whereas the remaining three showed a sharp aromatic proton singlet at G 7.26, 7.10, and 7.25 ppm. Comparison of these data with those reported in the literature revealed that the new anthraquinone corresponds to a combination of subunits -A (torosachrysone-8-O-methylether) and B (emodin-1-O-methyl ether) joined at the C-10c and C-5 position, respectively [6][7][8].

ABSTRACT

Biological control is a relatively cheap and most feasible long-term approach for controlling deadly weeds. Parthenium hysterophorus L. is a pernicious weed, imposing deleterious economic effects on humans and livestock. Microbial products thus offer a non-chemical alternative for controlling a noxious, invasive and pernicious weed like Parthenium. Phoma is a well-known phytopathogen responsible for many diseases in plants and is known to produce an array of bioactive extracellular toxic compounds, i.e. agribiologicals. Before application these have to be effectively formulated to enhance their absorption and translocation within the foliar tissues. Adjuvants are formulatives of microbial bioherbicides which ensure maximum herbicidal performance. Research on adjuvant and formulation technology for ecofriendly agrochemicals has advanced rapidly in recent years. Phytotoxins from Phoma sp. FGCC#18 have been tested for their compatibility with different formulants. Phytotoxicity damage was studied by seedling and detached leaf bioassays after different hours post-treatment. Tween 80 at 0.5% was found to be the best formulant, while the combination of Tween 80 and coconut oil at 0.5% exhibited maximum damage to Parthenium seedlings and detached leaves.

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